Optical properties of dissolved carbon in a high elevation tropical peatland ecosystem

Tropical peatlands are distributed mainly in coastal lowlands; however high elevation regions include a large prevalence of small and fragmented peatlands that are mostly understudied. Anthropogenic pressure to expand cattle farming, agriculture, and urbanization frontiers via artificial drainage of peatlands is increasing carbon losses to the atmosphere and streams. Here we present, the first characterization of dissolved carbon optical properties in ombrotrophic peat bogs of the Talamanca range of Costa Rica, across an altitudinal gradient (2,400-3,100 m asl) during the rainy season. Dissolved organic matter (DOM) sources and decomposition processes were evaluated in the light of dissolved organic and inorganic carbon (DOC and DIC), optical properties, excitation-emission matrices (EEMs), and major water chemistry. DOC concentrations ranged from 0.2 mg/L up to 47.0 mg/L, with a mean value of 12.5 ± 10.2 mg/L. DIC concentrations were below 2 mg/L and δ13CDIC values indicated a mixture between soil organic matter, CO2 in soil water, and in less degree DIC derived from bacterial CO2. Fluorescence intensity of humic-like peaks was 6-7 times greater than fresh-like peaks across all sites. Fluorescence peak ratios coupled with the biological and humification indexes point to a greater relative contribution of recalcitrant soil-derived DOM. EEMs denoted a high prevalence of humic and fulvic acids in the peat bogs, with particular high intensities in soluble microbial by-products-like and aromatic protein regions at three sites. Rainfall variability plays a remarkable role in controlling (acid and anoxic conditions) carbon storage and humification processes. Our data provides a baseline to underpin tropical carbon dynamics across high elevation peatlands.

热带泥炭地主要分布于沿海低地，但高海拔区域广泛分布着小型且碎片化的泥炭地，这类泥炭地大多尚未得到充分研究。人类通过人工排水手段扩张畜牧养殖、农业开发与城市化边界的活动压力，正不断加剧泥炭地向大气及溪流的碳流失。本研究首次对哥斯达黎加塔拉曼卡山脉海拔梯度（2400~3100 m asl）内的雨养泥炭沼泽（ombrotrophic peat bogs）中的溶解碳光学特性进行了表征，采样时段为雨季。本研究结合溶解有机碳（Dissolved Organic Carbon, DOC）、溶解无机碳（Dissolved Inorganic Carbon, DIC）、光学特性、激发发射矩阵光谱（Excitation-Emission Matrices, EEMs）以及主要水化学指标，对溶解态有机物（Dissolved Organic Matter, DOM）的来源与分解过程进行了评估。DOC浓度范围为0.2 mg/L至47.0 mg/L，平均值为12.5 ± 10.2 mg/L。DIC浓度低于2 mg/L，且δ¹³C_DIC值表明其来源为土壤有机质、土壤水中的CO₂，以及在较小程度上源自细菌代谢产生的CO₂所形成的DIC。所有采样点的类腐殖质峰荧光强度均为类新鲜物质峰的6~7倍。荧光峰比值结合生物学指数与腐殖化指数，表明难降解的土壤来源DOM占比相对更高。EEMs分析显示，该泥炭沼泽中腐殖酸与富里酸占比极高，其中3个采样点的可溶性微生物副产物类与芳香蛋白区域荧光强度尤为显著。降雨变异性在调控（酸性与缺氧环境下的）碳储存及腐殖化过程中发挥着显著作用。本研究数据为高海拔热带泥炭地的碳动态研究提供了基准基线。